Analog Multiplexer Core Circuit for High-Speed Linear Time-Multiplexing
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Solution Overview
Problem
Existing analog multiplexer circuits face challenges in achieving high-speed and high-linearity time-multiplexing of analog signals, with previous solutions either failing to maintain linearity at high speeds or experiencing waveform distortion due to restricted amplification.
Innovation Solution
The proposed analog multiplexer core circuit employs a fully differential structure with emitter-coupled logic and strategically placed emitter resistors to ensure linear response to analog signals, using a constant current source and emitter resistors that satisfy specific resistance and current value conditions to maintain linearity and support high-speed operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If FET gating is used for analog signal switching, then the circuit structure is simple, but the switching speed cannot reach high speed requirements
Solution Approach 1:
The patent replaces the mechanical FET gating switching mechanism with an emitter-coupled logic circuit using bipolar transistors. This substitution enables high-speed operation by utilizing the faster switching characteristics of bipolar transistors in emitter-coupled configuration, while maintaining circuit simplicity through the inherent switching functionality of the ELC structure.
2Speed
If emitter-coupled logic is used for high-speed operation, then switching speed is extremely high, but linearity is poor and waveform distortion occurs
Solution Approach 1:
The patent modifies the ELC circuit parameters by introducing emitter resistors with specifically designed resistance values. These resistors are calculated to provide adequate amplification for analog signals while maintaining the high-speed switching capability. The parameter optimization ensures that the transistors operate in a region that balances speed and linearity, reducing waveform distortion.
Solution Approach 2:
The patent introduces emitter resistors as intermediary elements between the transistor emitters and the current source. These resistors act as mediators that provide negative feedback, improving linearity by reducing the non-linear effects of the transistor characteristics, while minimally impacting the high-speed switching performance.
3Stability of the object's composition
If constant current source is used in ELC circuit, then switching operation is stable, but amplification of analog signals is restricted causing waveform distortion
Solution Approach 1:
The patent optimizes the constant current source parameters by carefully selecting the current value and adding emitter resistors. The emitter resistors provide local feedback that linearizes the current distribution, allowing adequate analog signal amplification while maintaining stable switching operations. The resistance values are specifically calculated to balance these competing requirements.
Data Source
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AI summary
An analog multiplexer core circuit (120A) includes a differential pair (121) that includes two transistors (Q1, Q2), a differential pair (122) that includes two transistors (Q3, Q4), a differential pair (123) that includes two transistors (Q5, Q6), and a constant current source (124) that causes a current (IEE) to flow. This analog multiplexer core circuit (120A) time-multiplexes two analog signals (Ain1, Ain2) and outputs a time-multiplexed analog signal (Aout). Each emitter resistor (REA1, REA2, REA3, REA4) is connected to a corresponding one of the transistors (Q1, Q2, Q3, Q4). At this time, a relation of "REA·IEE ≥ the amplitude of an input analog signal" is satisfied. As a result, linearity of response can be ensured by expanding the linear response input range of the differential pairs (121, 122).